cp-tree.h (default_hash_traits <lang_identifier *>): New specialization.

	* cp-tree.h (default_hash_traits <lang_identifier *>): New
	specialization.
	* name-lookup.c (lookup_extern_c_fun_in_all_ns): Delete.
	(extern_c_fns): New hash table.
	(check_extern_c_conflict): New, broken out of ...
	(pushdecl_maybe_friend_1): ... here.  Call it.
	(c_linkage_bindings): Just look in hash table.

From-SVN: r248159